Mori,
Rob (Toecutter here on the forum has already done all the hard work) I have posted him a kit piston a few months ago & he has been developing a set of standard 3 ring pistons & oversize 2 ring race pistons. These are a cnc machined forges pistons designed by some of the best piston engineers around.
The ART pistons are a cast piston & as such will not be as stable at high speed & temp.
The ones Rob have developed use the crown of the kit piston (13.0:1 according to the kit manual
http://www.zxrworld.co.uk/Manuals/zxr400r.pdf) & are lighter than the standard piston. They have coated skirts & use a thinner cast iron compression ring. They will make a set of JE's look like truck pistons.
I have posted some pictures & details of the kit pistons here,
viewtopic.php?f=117&t=10108, They were only available in standard bore size.
He has been working on these for the last three months & done a dummy assemblies to ensure clearances are spot on.
Considering the cost of all development work & pedigree of the company manufacturing these pistons the price is very reasonable.
Don't forget they include pistons, rings, pins & clips.
Regards,
Michael